Curable silicone compositions have been used in a wide range of industrial fields since the silicone compositions cure to form cured products having excellent heat resistance, cold resistance, electrical insulating properties, weatherability, water repellency, and transparency. In particular, the cured products thereof are less likely to be discolored and cause less degradation of physical properties compared to other organic materials. Therefore, the cured products are suitable as optical materials. For example, Patent Document 1 proposes a liquid silicone resin composition for light emitting diode (LED) elements, the liquid silicone resin composition comprising: an alkenyl group-containing silicone resin; a silicon atom-bonded hydrogen atom-containing organopolysiloxane; and a hydrosilylation catalyst.
On the other hand, in recent years, a material that is solid or semisolid at room temperature for a production process of a novel light emitting diodes (LEDs) has been proposed. For example, Patent Document 2 describes a sheet-like silicone resin composition for light emitting diodes (LEDs), the sheet-like silicone resin composition comprising: an alkenyl group-containing silicone resin; a silicon atom-bonded hydrogen atom-containing organopolysiloxane; and a hydrosilylation catalyst. Patent Document 3 describes a curable organopolysiloxane composition comprising: a solvent-soluble alkenyl group-containing organopolysiloxane formed by a hydrosilylation reaction of an alkenyl group-containing organopolysiloxane and a silicon atom-bonded hydrogen atom-containing organopolysiloxane; a silicon atom-bonded hydrogen atom-containing organopolysiloxane; and a hydrosilylation catalyst. Patent Document 4 describes a silicone resin sheet obtained by semi-curing a silicone resin composition comprising: an organopolysiloxane having at least two alkenylsilyl groups in a molecule; an organopolysiloxane having at least two hydrosilyl groups in a molecule; a hydrosilylation catalyst; and a reaction inhibitor.
However, these materials have problems of surface stickiness at 25° C. and insufficient hot-melt properties, and thus are not satisfactory for practical applications. Furthermore, as LED packages with higher brightness are realized, these materials have problems of insufficient heat resistance/light resistance although further heat resistance/light resistance has been demanded.